Semiconductor device and manufacturing method thereof

ABSTRACT

A method for forming a semiconductor device is provided. The method includes forming a first recess in a substrate. The method includes forming a first semiconductor layer into the first recess. The first semiconductor layer and the substrate are made of different materials, and a first top surface of the first semiconductor layer is lower than a second top surface of the substrate. The method includes forming a second semiconductor layer over the first top surface and the second top surface, wherein a third top surface of the second semiconductor layer over the first top surface is substantially level with the second top surface of the substrate, and the second semiconductor layer and the substrate are made of different materials. The method includes forming a third semiconductor layer over the second semiconductor layer. The third semiconductor layer and the second semiconductor layer are made of different materials.

RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 15/963,920, filed on Apr. 26, 2018, the entire ofwhich is incorporated by reference herein. The U.S. patent applicationSer. No. 15/963,920 claims priority to U.S. Provisional Application Ser.No. 62/593,143, filed Nov. 30, 2017, which is herein incorporated byreference.

BACKGROUND

Transistors are components of modern integrated circuits. To satisfy thetrend of increasingly faster speed, the drive currents of transistorsneed to be increasingly greater. To achieve this increase inperformance, the gate lengths of transistors are scaled down. Scalingdown the gate lengths leads to undesirable effects known as“short-channel effects,” in which the control of current flow by thegates is compromised. Among the short-channel effects are theDrain-Induced Barrier Lowering (DIBL) and the degradation ofsub-threshold slope, both of which result in the degradation in theperformance of transistors.

For example, multi-gate devices have been introduced in an effort toimprove gate control by increasing gate-channel coupling, reduceOFF-state current, and reduce short-channel effects (SCEs). One suchmulti-gate device is horizontal gate-all-around (HGAA) transistor, whosegate structure extends around its horizontal channel region providingaccess to the channel region on all sides or three sides. The HGAAtransistors are compatible with complementary metal-oxide-semiconductor(CMOS) processes, allowing them to be aggressively scaled down whilemaintaining gate control and mitigating SCEs. However, fabrication ofthe HGAA transistors can be challenging. For example, nanowire formationof HGAA transistors by the current methods is not satisfactory in allrespects, especially when using a single process, such as a singleepitaxial process.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying Figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure.

FIGS. 2-10 are cross-sectional views corresponding to line A-A of FIG. 1and show a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 11 is a cross-sectional view corresponding to line B-B of FIG. 1and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 12 is a cross-sectional view corresponding to line C-C of FIG. 1and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 13 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure.

FIGS. 14-22 are cross-sectional views corresponding to line A-A of FIG.13 and show a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 23 is a cross-sectional view corresponding to line B-B of FIG. 13and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 24 is a cross-sectional view corresponding to line C-C of FIG. 13and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure

FIG. 25 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure.

FIGS. 26-33 are cross-sectional views corresponding to line A-A of FIG.25 and show a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 34 is a cross-sectional view corresponding to line B-B of FIG. 25and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

FIG. 35 is a cross-sectional view corresponding to line C-C of FIG. 25and shows a sequential process for manufacturing a GAA FET deviceaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the Figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe Figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The gate all around (GAA) transistor structures may be patterned by anysuitable method. For example, the structures may be patterned using oneor more photolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers may then be used to pattern the GAA structure.

It is also noted that the present disclosure presents embodiments in theform of methods of forming semiconductor devices. For example,embodiments of the present disclosure may be used to form multi-gatetransistors such as FinFET devices, gate-all-around (GAA) devices,Omega-gate (a-gate) devices, or Pi-gate (H-gate) devices, as well asstrained-semiconductor devices, silicon-on-insulator (SOI) devices,partially-depleted SOI devices, fully-depleted SOI devices. In addition,embodiments disclosed herein may be employed in the formation of P-typeand/or N-type devices. One of ordinary skill may recognize otherembodiments of semiconductor devices that may benefit from aspects ofthe present disclosure.

FIG. 1 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure. FIGS. 2-12 show exemplary sequentialprocesses for manufacturing GAA FET devices according to embodiments ofthe present disclosure. It is understood that additional operations canbe provided before, during, and after processes shown by FIGS. 2-12, andsome of the operations described below can be replaced or eliminated,for certain embodiments of the method. The order of theoperations/processes may be interchangeable.

A plan view of a GAA FET device is illustrated in FIG. 1. As shown inFIG. 1, gate stacks 122 are formed overlying first and second nanowirestructures 124A and 124B, each of which includes one or more nanowires.Although two nanowire structures and two gate stacks are shown in FIG.1, GAA FET devices according to the present disclosure may include one,three, or more nanowire structures and one, three, or more gate stacks.

Referring to FIG. 2, a device 1 comprising a substrate 100 is provided.The substrate 100 may be a semiconductor substrate, which may be, forexample, a silicon substrate, a silicon germanium substrate, or asubstrate formed of other semiconductor materials. In some embodiments,the substrate 100 is a bulk substrate. Alternatively, the substrate 100may be a semiconductor-on-insulator (SOI) substrate. Hard mask 102 isformed over the substrate 100. In accordance with some embodiments ofthe present disclosure, the hard mask 102 is formed of silicon oxide,silicon nitride, silicon oxynitride, silicon carbide, siliconcarbo-nitride, the like, or combinations thereof.

As shown in FIG. 2, the substrate 100 comprises a P-type field effecttransistor (PFET) region 101 and an N-type field effect transistor(NFET) region 103. Next, as shown in FIG. 3, the hard mask 102 and thesubstrate 100 are patterned and etched to form a recess P1 over the NFETregion 103. Therefore, a top surface of the NFET region 103 is lowerthan that of the PFET region 101. In some embodiments, a silicongermanium (SiGe) layer 104 is then formed on the substrate 100 in theNFET region 103 to fill the recess P1, as shown in FIG. 4. In otherembodiments, the layer 104 may be made of other semiconductor materials.The silicon germanium layer 104 is different from the material of thesubstrate 100. For example, the substrate 100 is formed of silicon,rather than silicon germanium. The formation of the SiGe layer 104 maybe performed by a molecular beam epitaxy (MBE) process, a metalorganicchemical vapor deposition (MOCVD) process, and/or other suitable growthprocesses.

After the formation of the SiGe layer 104, a planarization operation,such as a chemical mechanical planarization (CMP) operation, may beperformed to the substrate 100, thinning down the SiGe layer 104overlying the substrate 100 in the NFET region 103. The resultingstructure is illustrated in FIG. 5. A top surface of the SiGe layer 104is substantially level with a top surface of the substrate 100 in thePFET region 101.

After the planarization operation performed to the SiGe layer 104, anetch-back operation is performed to recess the SiGe layer 104, therebyforming a lowered top surface S1 in lower elevation than the top surfaceS2 of the substrate 100 in the PFET region 101. The resulting structureis shown in FIG. 6. The recessing process may include a dry etchingprocess, a wet etching process, and/or a combination thereof. Conditionsof the recessing process are selected to form such surfaces S1 and S2 asshown in FIG. 6. For example, the etch-back operation may be a plasmaprocess using CF₄, CF₂Cl₂, CF₃Br, HBr, chlorine as process gases and aninert gas, such as He, Ne, Ar, Kr, Xe and Rn and combinations thereof asa carrier gas, to anisotropically etch the SiGe layer 104. In someembodiments, the etch-back operation comprises adoping an etchant havinga selectivity between Si and SiGe. In some embodiments, the processconditions include a temperature of below about 200° C., a pressure fromabout 0 torr to about 10 torr, and an RF power of from about 50 W toabout 2000 W. In other embodiments, the process conditions include atemperature of below about 60° C., a pressure of from about 0 torr toabout 500 mtorr, and an RF power from about 50 W to about 300 W. In someembodiments, the etch-back may be performed using first standardcleaning (SC1), second standard cleaning (SC2) and etching gases, whichmay be HCl. An exemplary SC1 employs a cleaning solution, such asammonia hydroxide-hydrogen peroxide-water mixture, which is applied attemperature from about 20° C. to about 100° C. and under pressure about1 torr. An exemplary SC2 employs another cleaning solution, such ashydrochloric acid-hydrogen peroxide-water mixture, which is applied attemperature from about 20° C. to about 100° C. and under pressure about1 torr. While using HCl as etching gases to perform the etch-back, theflow rate of HCl is from about 100 sccm to about 30000 sccm. Theetch-back temperature is from about 500° C. to about 600° C. Thepressure is from about 10 torr to about 100 torr.

Referring to FIG. 6, in some embodiments, a recessing depth of the SiGelayer 104 is controlled (e.g., by controlling an etching duration) so asto result in a desired height difference between the top surface S1 ofthe remaining SiGe layer 104 and the top surface S2 of the substrate 100in the PFET region 101. The height difference between the top surfacesS1 and S2 may be adjusted based on heights of nanowires subsequentlyformed in the PFET region 101 and the NFET region 103. In someembodiments, the height difference between the top surfaces S1 and S2ranges from about 4 nm to about 10 nm. Such a height differencecontributes to alignment of subsequently formed Si nanowires in the NFETregion 103 with SiGe nanowires in the PFET region 101.

A stack including semiconductor layers are formed over the substrate.For example, referring to FIG. 7, a first stack 105 and a second stack107 of semiconductor layers are formed over the substrate 100 in thePFET region 101 and the NFET region 103 respectively. The first stack105 and second stack 107 of semiconductor layers may include alternatinglayers of different compositions. For example, in some embodiments, thefirst and second stacks 105 and 107 include first semiconductor layers106 of a first composition alternating with second semiconductor layers108 of a second composition different from the first composition.Although five first semiconductor layers 106 and five secondsemiconductor layers 108 are shown, it is understood that the first andsecond stacks 105 and 107 may include any number of layers of anysuitable composition with various examples including between 2 and 10first semiconductor layers 106 and between 2 and 10 second semiconductorlayers 108. As explained below, the different compositions of the layersin the first and second stacks 105 and 107 (e.g., first semiconductorlayers 106 and second semiconductor layers 108) may be used toselectively process some of the layers. Accordingly, the compositionsmay have different oxidation rates, etchant sensitivity, and/or otherdiffering properties.

In some embodiments, either of the semiconductor layers 106 and 108 mayinclude silicon. In some embodiments, either of the semiconductor layers106 and 108 may include other materials such as Ge, a compoundsemiconductor such as silicon carbide, gallium arsenide, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide,an alloy semiconductor such as SiGe, GaAsP, AlInAs, AlGaAs, InGaAs,GaInP, and/or GaInAsP, or combinations thereof. In some embodiments, thesemiconductor layer 106 may include from about 10% to about 70% Ge inmolar ratio and the semiconductor layer 108 may include Si. In otherembodiments, the semiconductor layer 106 may include Si and thesemiconductor layer 108 may include from about 10% to about 70% Ge inmolar ratio. In some embodiments, the semiconductor layers 106 and 108may be undoped or substantially dopant-free (i.e., having an extrinsicdopant concentration from about 0 cm⁻³ to about 1×10¹⁷ cm⁻³), where forexample, no doping is performed during the epitaxial growth process.Alternatively, the semiconductor layers 108 may be doped. For example,the semiconductor layers 106 or 108 may be doped with a p-type dopantsuch as boron (B), aluminum (Al), indium (In), and gallium (Ga) forforming a p-type channel, or an n-type dopant such as phosphorus (P),arsenic (As), antimony (Sb), for forming an n-type channel. In thedepicted embodiments, the first semiconductor layers 106 are SiGelayers, and the second semiconductor layer 108 are Si layers.

The thickness of first and second semiconductor layers 106 and 108 aredetermined based on the height difference between the top surfaces S1and S2. For example, the thickness of either the first semiconductorlayer 106 or the second semiconductor layer 108 is substantially equalto the height difference between the top surfaces S1 and S2. By way ofexample, the thickness of the first semiconductor layer 106 is in arange from about 4 nm to about 10 nm. In some embodiments, the firstsemiconductor layers 106 of the first and second stacks 105 and 107 maybe substantially uniform in thickness. In some embodiments, thethickness of the semiconductor layer 108 is in a range from about 4 nmto about 10 nm. In some embodiments, the second semiconductor layers 108of the first and second stacks 105 and 107 are substantially uniform inthickness. By way of example, growth of the layers of the stacks 105 and107 may be performed by a molecular beam epitaxy (MBE) process, ametalorganic chemical vapor deposition (MOCVD) process, and/or othersuitable epitaxial growth processes. In some embodiments, the growth ofthe layers of the stacks 105 and 107 may be performed using processgases comprising SiH₄, DCS, GeH₄, Si₂H₆, PH₃, HCl, GeH₄ or MMS (carbonsource) and carrier gas comprising N₂ or H₂. The epitaxial growthprocess may be performed under process temperature in a range from about400° C. to about 800° C. and under process pressure below about 50 torr,as example.

Referring again to FIG. 7, the stacks 105 and 107 are grown using asingle epitaxial process. In other words, the stacks 105 and 107 areepitaxially grown simultaneously over the PFET and NFET region 101 and103. Since the height difference between the top surfaces S1 and S2 isequal to the thickness of either the first semiconductor layer 106 orthe second semiconductor layer 108, a bottommost semiconductor layer 106in the NFET region 103 has a top surface substantially level with thetop surface S2 of the substrate 100 in the PFET region 101. Therefore,the first semiconductor layers 106 in the PFET region 101 are alignedwith the respective semiconductor layers 108 in the NFET region 103.Meanwhile, the semiconductor layers 108 in the PFET region 101 arealigned with the respective semiconductor layers 106 in the NFET region103.

In some embodiments, a bottommost semiconductor layer 106 overlying thesubstrate 100 in the PFET region 101 is at a height higher than abottommost semiconductor layer 106 overlying the SiGe layer 104 in theNFET region 103, as shown in FIG. 7. Therefore, a top surface of thefirst stack 105 is at a height higher than a top surface of the secondstack 107. In detail, a height difference between a top surface of thestack 105 and a top surface of the stack 107 is substantially equal tothe height difference between the top surfaces S1 and S2. In otherwords, the semiconductor layer 108 overlying the substrate 100 in thePFET region 101 is at a height higher than the semiconductor layer 108overlying the SiGe layer 104 in the NFET region 103.

Next, referring to FIG. 8, first and second fin elements 110A and 110Bare formed over the PFET region 101 and the NFET region 103 usingsuitable processes including photolithography and etch processes. Insome embodiments, a photoresist is formed over the first and secondstacks 105 and 107 (as shown in FIG. 7) and patterned using alithography process. The patterned photoresist may then be used toprotect regions of the substrate 100 and the SiGe layer 104, and layersformed thereupon, while an etch process forms trenches in unprotectedregions through the photoresist, through the stacks 105 and 107, andinto the substrate 100 and the SiGe layer 104. The remaining portions ofthe stacks 105 and 107 can serve as fin elements 110A and 110B thatinclude the semiconductor layers 106 and 108. In some embodiments, thepatterns in photoresist are controlled so as to result in a desiredwidth of the fin elements 110A and 110B. The width may be chosen basedon device performance considerations. In some embodiments, the first finelement 110A is a portion of a P-type metal-oxide semiconductor (PFET)device, and the second fin element 110B is a portion of an N-typemetal-oxide semiconductor (NFET) device. As illustrated in FIG. 8, thefirst fin element 110A extends upwardly from the PFET region 101 of thesubstrate 100, and the second fin element 110B extends upwardly from theNFET region 103 of the substrate 100.

FIG. 8 also illustrates isolation regions 109 between the first andsecond fin elements 110A and 110B. An exemplary formation of theisolation regions 109 includes depositing a dielectric material, such assilicon oxide, into the trenches between the fin elements 110A and 110Bto form isolation regions 109, planarizing the isolation regions 109 byusing, for example, a chemical mechanical planarization (CMP) operation,and then recessing the isolation regions 109, such that the isolationregions 109 have top surfaces in positions lower than top surfaces ofthe fin elements 110A and 110B. In some embodiments, the recessing theisolation regions 109 may include a dry etching process, a wet etchingprocess, and/or a combination thereof. In some embodiments, a recessingdepth is controlled (e.g., by controlling an etching time) so as toresult in a desired height of portions of the fin elements 110A and 110Bprotruding above the isolation regions 109. The height may be chosenbased on device performance considerations.

Referring to FIG. 9, the second semiconductor layers 108 in the PFETregion 101 and the first semiconductor layers 106 in the NFET region 103are removed using suitable etch techniques. For example, the secondsemiconductor layers 108 in the PFET region 101 are removed by using afirst etching process, and the first semiconductor layers 106 in theNFET region 103 are removed by using a second etching process differentfrom the first etching process. In some embodiments, an etch rate ofsilicon is greater than an etch rate of silicon germanium during thefirst etching process, so that the silicon layers 108 in the PFET region101 are selectively removed. On the contrary, an etch rate of silicongermanium is greater than an etch rate of silicon during the secondetching process, so that the silicon germanium layers 106 in the NFETregion 103 are selectively removed. In some embodiments, the etchantused in the second etching process may include Cl₂, NF₃ and He mixture,an alkali solution (for example, such as NH₄OH or TMAH), F₂/NH₃ mixture,SF₆, CH₃F or other etchant which provides comparable etch rate than theetchant used in the first etching process. In other embodiments, theetchant used in the second etching process may include halogen and/orcomposition used for passivation. In some embodiments, the secondetching process may be performed at temperature below about 100° C.Embodiments of the present disclosure may employ a patterned mask toprotect a region (e.g. NFET region 103) when certain semiconductorlayers in another region (e.g. PFET region 101) are to be removed.

In the following discussion, the remaining semiconductor layers 106 ofthe fin elements 110A are referred to as first nanowires 116A. In someembodiments, as shown in FIG. 9, the nanowires 116A have across-sectional profile of a rectangle and are suspended. Gaps 117A areformed between adjacent nanowires 116A. In addition, immediatelyadjacent nanowires 116A are spaced-apart by a substantially equaldistance.

In the following discussion, the remaining semiconductor layers 108 ofthe fin elements 110B in the NFET region 103 are referred to as thenanowires 116B. In some embodiments, as shown in FIG. 9, nanowires 116Bhave a cross-sectional profile of a rectangle and are suspended.Immediately adjacent nanowires 116B may be spaced-apart by gaps 117Bformed between adjacent nanowires 116B. In addition, immediatelyadjacent nanowires 116B are spaced-apart by a substantially equaldistance.

The nanowires 116A in the PFET region 101 are aligned with the nanowires116B in the NFET region 103, as shown in FIG. 9, which in turn willreduce potential loading effects in subsequent processes (e.g. formationof gate stacks). In some embodiments, the bottommost nanowire 116A inthe PFET region 101 is suspended. In other words, the bottom surface ofthe bottommost nanowire 116A is separated from the underlying material.That is, the bottommost nanowire 116A is not in physical contact withthe substrate 100. In some embodiments, the bottommost nanowire 116B inthe NFET region 103 is suspended as well. In other words, the bottommostnanowire 116B is not in physical contact with the SiGe layer 104. Suchsuspended nanowires in PFET and NFET regions 101 and 103 areadvantageous for improving device performance, which will be discussedbelow.

In some embodiments, as shown in FIG. 9, the nanowires 116A and 116Bhave a profile of the same shape (e.g., rectangle in cross section).Alternatively, in some embodiments, the nanowires 116A and 116B may haveprofiles of different shapes. In some embodiments, the etchingconditions of the etching process may be controlled so that thenanowires 116A and 116B have desired nanowire widths and desirednanowire heights, and adjacent nanowires 116A, 116B have desired spacingdistances. The various desired dimensions and shapes may be chosen basedon device performance considerations.

Next, a first gate stack 122A is formed around each first nanowires116A, and a second gate stack 122B is formed around each second nanowire116B. The gate stacks are formed around a central portion of thenanowires that is channel regions of the nanowires. The gate stack 122Aincludes a gate dielectric layer 118A formed around nanowires 116A and agate electrode layer 120A formed around the gate dielectric layer 118A,in some embodiments. The gate stack 122B includes a gate dielectriclayer 118B formed around nanowires 116B and a gate electrode layer 120Bformed around the gate dielectric layer 118B, in some embodiments.

In certain embodiments, at least one of the gate dielectric layers 118Aand 118B includes one or more layers of a dielectric material, such assilicon oxide, silicon nitride, high-k dielectric material, othersuitable dielectric material, and any combination thereof. Examples ofhigh-k dielectric material include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO,HfZrO, zirconium oxide, aluminum oxide, titanium oxide, hafniumdioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-k dielectricmaterials, or any combination thereof. In some embodiments, the gatedielectric layer includes an interfacial layer (not shown) formedbetween the nanowires and the dielectric material. The gate dielectriclayer may be formed by CVD, ALD, or any suitable method. In oneembodiment, the gate dielectric layer is formed using a highly conformaldeposition process such as ALD in order to ensure the formation of agate dielectric layer having a uniform thickness around each nanowire.

At least one of the gate electrode layers 120A and 120B includes one ormore layers of conductive material, such as polysilicon, aluminum,copper, titanium, tantalum, tungsten, cobalt, molybdenum, tantalumnitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN,TaC, TaSiN, metal alloys, other suitable materials, or any combinationthereof. The gate electrode layer may be formed by CVD, ALD,electroplating, or other suitable method. In some embodiments, the gateelectrode layers 120A and 120B are formed of different metals, so thatthe gate electrode layer 120A can provide suitable work function for thePFET device, and the gate electrode layer 120B can provide suitable workfunction for the NFET device.

In some embodiments, insulating sidewalls 119 are formed on opposingsides of the gate electrode layers 120A and 120B, and first source/drainlayers 115A are formed on peripheral portions of the nanowires 116A andon opposing sides of the gate stack 122A. The insulating sidewall 119 isbetween the gate stack 122A and the source/drain layer 115A, as shown inFIG. 11, which corresponds to a cross section according to line B-B ofFIG. 1 of the first nanowire structure 124A. Similarly, secondsource/drain layers 115B are formed on peripheral portions of thenanowires 116B and on opposing sides of the gate stack 122B. Theinsulating sidewall 119 is between the gate stack 122B and thesource/drain layer 115B, as shown in FIG. 12, which corresponds to across section according to line C-C of FIG. 1 of the second nanowirestructure 124B.

By way of example, the material for the source/drain layers 115Aincludes one or more layers of Ge or SiGe suitable for the PFET device,and material for the source/drain layers 115B includes one or morelayers of Si, SiP, or SiC suitable for the NFET device. The source/drainlayers 115A and 115B are formed by an epitaxial growth method using CVD,ALD, or molecular beam epitaxy (MBE). During formation of source/drainlayer 115A for the PFET device, the second nanowires 116B in the NFETregion 103 are covered by a patterned mask. During formation of thesource/drain layer 115B for the NFET device, the first nanowires 116A ofthe PFET device is covered by another patterned mask.

In order to support the nanowires during processing, the peripheralportions of the nanowires where the source/drain layers 115A and 115Bare formed may be masked during the removal of either the first andsecond semiconductor layers 106 and 108 from the central portions of thenanowires where the gate stacks 122A and 122B are to be formed. Afterformation of the gate stacks 122A and 122B, the central portion of thenanowires where the gate stacks 122A and 122B are formed may be masked,and the respective first and second semiconductor layers 106 and 108 areremoved from the peripheral portions of the nanowire where thesource/drain layers 115A and 115B are formed.

Alternatively, in some embodiments dummy gate structures are initiallyformed on the first and second fin elements 110A and 110B (see FIG. 8),and the respective first and second semiconductor layers 106 and 108 areremoved from the peripheral portions of the nanowire where thesource/drain layers 115A and 115B are formed. After forming thesource/drain layers 115A and 115B, the dummy gate electrode structuresare removed, followed by formation of gate stacks 122A and 122Baccording to the present disclosure.

FIG. 13 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure. FIGS. 14-24 show exemplary sequentialprocesses for manufacturing GAA FET devices according to embodiments ofthe present disclosure. It is understood that additional operations canbe provided before, during, and after processes shown by FIGS. 14-24,and some of the operations described below can be replaced oreliminated, for certain embodiments of the method. The order of theoperations/processes may be interchangeable.

A plan view of a GAA FET device is illustrated in FIG. 13. As shown inFIG. 13, gate stacks 222 are formed overlying first and second nanowirestructures 224A and 224B, each of which includes one or more nanowires.Although two nanowire structures and two gate stacks are shown in FIG.13, GAA FET devices according to the present disclosure may include one,three, or more nanowire structures and one, three, or more gate stacks.Referring to FIG. 14, a device 2 comprising a substrate 200 is provided.The substrate 200 may be semiconductor substrate, which may be, forexample, a silicon substrate, a silicon germanium substrate, or asubstrate formed of other semiconductor materials. In some embodiments,substrate 200 is a bulk substrate. Alternatively, the substrate 200 maybe a semiconductor-on-insulator (SOI) substrate. Hard mask 202 is formedover the substrate 200. In accordance with some embodiments of thepresent disclosure, the hard mask 202 is formed of silicon nitride,silicon oxynitride, silicon carbide, silicon carbo-nitride, the like, orcombinations thereof.

As shown in FIG. 14, the substrate 200 comprises a PFET region 201 andan NFET region 203. Next, as shown in FIG. 15, the hard mask 202 and thesubstrate 200 are patterned and etched to form a recess P2 over the NFETregion 203. Therefore, a top surface of the NFET region 203 is lowerthan that of the PFET region 201. In some embodiments, a silicongermanium (SiGe) layer 204 is formed on the substrate 200 in the NFETregion 203 to fill the recess P2, as shown in FIG. 16. The silicongermanium layer 204 is different from the material of the substrate 200.For example, the substrate 200 is formed of silicon, rather than silicongermanium. The formation of the SiGe layer 204 may be performed by amolecular beam epitaxy (MBE) process, a metalorganic chemical vapordeposition (MOCVD) process, and/or other suitable growth processes.

After the formation of the SiGe layer 204, an optional planarizationoperation, such as a chemical mechanical planarization (CMP) operation,may be performed to the substrate 200, thinning down the SiGe layer 204overlying the substrate 200 in the NFET region 203. The resultingstructure is illustrated in FIG. 17. A top surface of the SiGe layer 204is substantially level with a top surface of the substrate 200 in thePFET region 201.

After the planarization operation performed to the SiGe layer 204, anetch-back operation is performed to recess the Si substrate 200 in thePFET region 201 before the subsequent epitaxial growth process, therebyforming a lowered top surface S4 in lower elevation than a top surfaceS3 of the SiGe layer 204 in the NFET region 203. The resulting structureis shown in FIG. 18. The recessing process may include a dry etchingprocess, a wet etching process, and/or a combination thereof. Conditionsof the recessing process are selected to form such surfaces S3 and S4 asshown in FIG. 18. For example, the etch-back operation may be a plasmaprocess using CF₄, CF₂Cl₂, CF₃Br, HBr, chlorine as process gases and aninert gas, such as He, Ne, Ar, Kr, Xe and Rn and combinations thereof asa carrier gas, to anisotropically etch the SiGe layer 204. In someembodiments, the etch-back operation comprises adopting an etchanthaving a selectivity between Si and SiGe, such that an etch rate of Siis higher than an etch rate of SiGe during this etch-back operation.

Referring to FIG. 18, in some embodiments, a recessing depth iscontrolled (e.g., by controlling an etching time) so as to result in adesired height difference between the top surface S3 of the SiGe layer204 and the top surface S4 of the substrate 200 in the PFET region 201.The height difference between the top surfaces S3 and S4 may be chosenbased on heights of nanowires subsequently formed in the PFET region 201and the NFET region 203. In some embodiments, the height differencebetween the top surfaces S3 and S4 ranges from about 4 nm to about 10nm. Such a height difference contributes to alignment of subsequentlyformed Si nanowires in the NFET region 203 with SiGe nanowires in thePFET region 201.

A stack including semiconductor layers are formed over the substrate.For example, referring to FIG. 19, a first stack 205 and a second stack207 of semiconductor layers are formed over the substrate 200 in thePFET region 201 and the NFET region 203 respectively. The first stack205 and second stack 207 of semiconductor layers may include alternatinglayers of different compositions. For example, in some embodiments, thefirst and second stacks 205 and 207 include first semiconductor layers206 of a first composition alternating with second semiconductor layers208 of a second composition different from the first composition.Although five first semiconductor layers 206 and five secondsemiconductor layers 208 are shown, it is understood that the first andsecond stacks 205 and 207 may include any number of layers of anysuitable composition with various examples including between 2 and 10first semiconductor layer 206 and between 2 and 10 second semiconductorlayers 208. As explained below, the different compositions of the layersin the first and second stacks 205 and 207 (e.g., first semiconductorlayers 206 and second semiconductor layers 208) may be used toselectively process some of the layers. Accordingly, the compositionsmay have different oxidation rates, etchant sensitivity, and/or otherdiffering properties.

In some embodiments, either of the semiconductor layers 206 and 208 mayinclude silicon. In some embodiments, either of the semiconductor layers206 and 208 may include other materials such as Ge, a compoundsemiconductor such as silicon carbide, gallium arsenide, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide,an alloy semiconductor such as SiGe, GaAsP, AlInAs, AlGaAs, InGaAs,GaInP, and/or GaInAsP, or combinations thereof. In some embodiments, thesemiconductor layer 206 may include from about 10% to about 70% Ge inmolar ratio and the semiconductor layer 208 may include Si. In otherembodiments, the semiconductor layer 206 may include Si and thesemiconductor layer 208 may include from about 10% to about 70% Ge inmolar ratio. In some embodiments, the semiconductor layers 106 and 108may be undoped or substantially dopant-free (i.e., having an extrinsicdopant concentration from about 0 cm⁻³ to about 1×10¹⁷ cm⁻³), where forexample, no doping is performed during the epitaxial growth process.Alternatively, the semiconductor layers 208 may be doped as discussedpreviously. In the depicted embodiments, the first semiconductor layers206 are SiGe layers, and the second semiconductor layers 208 are Silayers.

The thickness of first and second semiconductor layers 206 and 208 areformed based on the height difference between the top surfaces S3 andS4. For example, the thickness of either the semiconductor layer 206 orthe semiconductor layer 208 is substantially equal to the heightdifference between the top surfaces S3 and S4. By way of example, thethickness of the first semiconductor layer 206 is in a range from about4 nm to about 10 nm. In some embodiments, the first semiconductor layers206 of the first and second stacks 205 and 207 may be substantiallyuniform in thickness. In some embodiments, the thickness of thesemiconductor layer 208 is in a range from about 4 nm to about 10 nm. Insome embodiments, the second semiconductor layers 208 of the first andsecond stacks 205 and 207 are substantially uniform in thickness. By wayof example, growth of the layers of the stacks 205 and 207 may beperformed by a molecular beam epitaxy (MBE) process, a metalorganicchemical vapor deposition (MOCVD) process, and/or other suitableepitaxial growth processes. In some embodiments, the growth of thelayers of the stacks 205 and 207 may be performed using process gasescomprising SiH₄, DCS, GeH₄, Si₂H₆, PH₃, HCl, GeH₄ or MMS (carbon source)and carrier gas comprising N₂ or H₂. The epitaxial growth process may beperformed under process temperature in a range from about 400° C. toabout 800° C. and under process pressure below about 50 torr, asexample.

Referring again to FIG. 19, the stacks 205 and 207 are grown using asingle epitaxial process. In other words, the stacks 205 and 207 areepitaxially grown simultaneously over the substrate 200 and the SiGelayer 204. Since the height difference between the top surfaces S3 andS4 is equal to the thickness of either the first semiconductor layer 206or the second semiconductor layer 208, a bottommost semiconductor layer206 in the PFET region 201 has a top surface substantially level withthe top surface S3 of the SiGe layer 204 in the NFET region 203.Therefore, other first semiconductor layers 206 in the PFET region 201are aligned with the respective second semiconductor layers 208 in theNFET region 203. Meanwhile, the second semiconductor layers 208 in thePFET region 201 are aligned with the respective first semiconductorlayers 206 in the NFET region 203. In some embodiments, a bottommostsemiconductor layer 206 overlying the substrate 200 in the PFET region201 is at a height lower than a bottommost semiconductor layer 206overlying the SiGe layer 204 in the NFET region 203, as shown in FIG.19. Therefore, a top surface of the first stack 205 is at a height lowerthan a top surface of the second stack 207. In detail, a heightdifference between a top surface of the stack 205 and a top surface ofthe stack 207 is substantially equal to the height difference betweenthe top surfaces S3 and S4. In other words, the semiconductor layer 208overlying the substrate 200 in the PFET region 201 is at a height lowerthan the semiconductor layer 208 overlying the SiGe layer 204 in theNFET region 203.

Next, referring to FIG. 20, first and second fin elements 210A and 210Bare formed over the PFET region 201 and the NFET region 203 usingsuitable processes including photolithography and etch processes. Insome embodiments, a photoresist is formed over the first and secondstacks 205 and 207 (as shown in FIG. 19) and patterned using alithography process. The patterned photoresist may then be used toprotect regions of the substrate 200 and the SiGe layer 204, and layersformed thereupon, while an etch process forms trenches in unprotectedregions through the photoresist, through the stacks 205 and 207, andinto the substrate 200 and the SiGe layer 204. The remaining portions ofthe stacks 205 and 207 can serve as fin elements 210A and 210B thatinclude the semiconductor layers 206 and 208. In some embodiments, thepatterns in photoresist are controlled so as to result in a desiredwidth of the fin elements 210A and 210B. The width may be chosen basedon device performance considerations. In some embodiments, the first finelement 210A is a portion of P-type metal-oxide semiconductor (PFET)elements, and second fin element 210B is a portion of N-type metal-oxidesemiconductor (NFET) elements. As illustrated in FIG. 20, the first finelement 210A extends from the PFET region 201 of the substrate 200, andthe second fin element 210B extends from the NFET region 203 of thesubstrate 200.

Isolation regions 209 are formed, as shown in FIG. 20. For example, adielectric material, such as silicon oxide, may be deposited into thetrenches between the fin elements 210A and 210B to form isolationregions 209. A chemical mechanical planarization (CMP) operation may beperformed to planarize a top surface of the isolation regions 209, andthen the isolation regions 209 are recessed, thereby leaving the finelements 210A and 210B extending above the isolation regions 209. Insome embodiments, the recessing process may include a dry etchingprocess, a wet etching process, and/or a combination thereof. In someembodiments, a recessing depth is controlled (e.g., by controlling anetching time) so as to result in a desired height of portions of the finelements 210A and 210B protruding above the isolation regions 209. Theheight may be chosen based on device performance considerations.

Referring to FIG. 21, the second semiconductor layers 108 in the PFETregion 201 and the first semiconductor layers 206 in the NFET region 203are removed using suitable etch techniques. For example, the secondsemiconductor layers 208 in the PFET region 201 are removed by using afirst etching process, and the first semiconductor layers 206 in theNFET region 203 are removed by using a second etching process differentfrom the first etching process. In some embodiments, an etch rate ofsilicon is greater than an etch rate of silicon germanium during thefirst etching process, so that the silicon layers 208 in the PFET region201 are selectively removed. On the contrary, an etch rate of silicongermanium is greater than an etch rate of silicon during the secondetching process, so that the silicon germanium layers 206 in the NFETregion 203 are selectively removed. Embodiments of the presentdisclosure may employ a patterned mask to protect a region (e.g. NFETregion 203) when certain semiconductor layers in another region (e.g.PFET region 201) are to be removed.

In the following discussion, the remaining semiconductor layers 206 ofthe fin elements 210A are referred to as first nanowires 216A. In someembodiments, as shown in FIG. 21, the nanowires 216A have across-sectional profile of a rectangle and are suspended. Gaps 217A areformed between adjacent nanowires 216A. In addition, immediatelyadjacent nanowires 216A are spaced-apart by a substantially equaldistance.

In the following discussion, the remaining semiconductor layers 2108 ofthe fin elements 210B in the NFET region 203 are referred to as thenanowires 216B. In some embodiments, as shown in FIG. 21, nanowires 216Bhave a cross-sectional profile of a rectangle and are suspended.Immediately adjacent nanowires 216B may be spaced-apart by gaps 217Bformed between adjacent nanowires 216B. In addition, immediatelyadjacent nanowires 216B are spaced-apart by a substantially equaldistance. The nanowires 216A in the PFET region 201 are aligned with thenanowires 216B in the NFET region 203, as shown in FIG. 21, which inturn will reduce potential loading effects in subsequent processes (e.g.formation of gate stacks).

Next, a first gate stack 222A is formed around each first nanowires216A, and a second gate stack 222B is formed around each second nanowire216B. The gate stacks are formed around a central portion of thenanowires that is channel regions of the nanowires. The gate stack 222Aincludes a gate dielectric layer 218A formed around nanowires 216A and agate electrode layer 220A formed around the gate dielectric layer 218A,in some embodiments. The gate stack 222B includes a gate dielectriclayer 218B formed around nanowires 216B and a gate electrode layer 220Bformed around the gate dielectric layer 218B, in some embodiments.

In certain embodiments, at least one of the gate dielectric layers 218Aand 218B includes one or more layers of a dielectric material, asdiscussed with respect to the gate dielectric layers 118A and 118B. Atleast one of the gate electrode layers 220A and 220B includes one ormore layers of conductive material, as discussed with respect to thegate electrode layer 120A and 120B.

In some embodiments, insulating sidewalls 219 are formed on opposingsides of the gate stacks 222A and 222B, and first source/drain layers215A are formed on peripheral portions of the nanowires 216A and onopposing sides of the gate stack 222A. The insulating sidewall 119 isbetween the gate stack 222A and the source/drain layer 215A, as shown inFIG. 23, which corresponds to a cross section according to line B-B ofFIG. 13 of the first nanowire structure 224A. Similarly, secondsource/drain layers 215B are formed on peripheral portions of thenanowires 216B and on opposing sides of the gate stack 222B. Theinsulating sidewall 119 is between the gate electrode layer 220B and thesource/drain layer 215B, as shown in FIG. 24, which corresponds to across section according to line C-C of FIG. 13 of the second nanowirestructure 224B.

By way of example, the material for the source/drain layers 215Aincludes one or more layers of Ge or SiGe suitable for the PFET device,and material for the source/drain layers 215B includes one or morelayers of Si, SiP, or SiC suitable for the NFET device. The source/drainlayers 215A and 215B are formed by an epitaxial growth method using CVD,ALD, or molecular beam epitaxy (MBE). During formation of thesource/drain layer 215A for the PFET device, the second nanowires 216Bin the NFET region 203 are covered by a patterned mask. During formationof the source/drain layer 215B for the NFET device, the first nanowires216A of the PFET device are covered by another patterned mask.

In order to support the nanowires during processing, the peripheralportions of the nanowires where the source/drain layers 215A and 215Bare formed may be masked during the removal of either the first andsecond semiconductor layers 206 and 208 from the central portions of thenanowires where the gate stacks 222A and 222B are to be formed. Afterformation of the gate stacks 222A and 222B, the central portion of thenanowires where the gate stacks 222A and 222B are formed may be masked,and the respective first and second semiconductor layers 206 and 208 areremoved from the peripheral portions of the nanowire where thesource/drain layers 215A and 215B are formed.

Alternatively, in some embodiments dummy gate structures are initiallyformed on the first and second fin elements 210A and 210B (see FIG. 20),and the respective first and second semiconductor layers 206 and 208 areremoved from the peripheral portions of the nanowire where thesource/drain layers 215A and 215B are formed. After forming thesource/drain layers 215A and 215B, the dummy gate electrode structuresare removed, followed by formation of gate stacks 222A and 222Baccording to the present disclosure.

FIG. 25 is a plan view of some embodiments of a GAA FET device accordingto the present disclosure. FIGS. 26-35 show exemplary sequentialprocesses for manufacturing GAA FET devices according to embodiments ofthe present disclosure. It is understood that additional operations canbe provided before, during, and after processes shown by FIGS. 26-35,and some of the operations described below can be replaced oreliminated, for certain embodiments of the method. The order of theoperations/processes may be interchangeable.

A plan view of a GAA FET device is illustrated in FIG. 25. As shown inFIG. 25, gate stacks 318 are formed overlying first and second nanowirestructures 324A and 324B, each of which includes one or more nanowires.Although two nanowire structures and two gate stacks are shown in FIG.25, GAA FET devices according to the present disclosure may include one,three, or more nanowire structures and one, three, or more gate stacks.Referring to FIG. 26, a device 3 comprising a substrate 300 is provided.The substrate 300 may be semiconductor substrate, as previouslydiscussed with respect to the substrate 100 or 200. Hard mask 302 isformed over the substrate. In accordance with some embodiments of thepresent disclosure, the hard mask 302 is formed of silicon nitride,silicon oxynitride, silicon carbide, silicon carbo-nitride, the like, orcombinations thereof.

As shown in FIG. 26, the substrate 300 comprises a PFET region 301 and aNFET region 303. Next, as shown in FIG. 27, the hard mask 302 and thesubstrate 300 are patterned and etched to form a recess P3 over the NFETregion 303. Therefore, a top surface of the NFET region 303 is lowerthan that of the PFET region 301. In some embodiments, a silicongermanium (SiGe) layer 304 is formed on the substrate 300 in the NFETregion 303 to fill the recess P3, as shown in FIG. 28. The silicongermanium layer 304 is different from the material of the substrate 300.For example, the substrate 300 is formed of silicon, rather than silicongermanium. The formation of the SiGe layer 304 may be performed by amolecular beam epitaxy (MBE) process, a metalorganic chemical vapordeposition (MOCVD) process, and/or other suitable growth processes.

After the formation of the SiGe layer 304, a planarization operation,such as a chemical mechanical planarization (CMP) operation, may beperformed to the substrate 300, partially removing the SiGe layer 304overlying the substrate 300 in the NFET region 303. The resultingstructure is illustrated in FIG. 29. A top surface of the SiGe layer 304is substantially level with a top surface of the substrate 300 in thePFET region 301.

A stack including semiconductor layers are formed over the substrate.For example, referring to FIG. 30, a first stack 305 and a second stack307 of semiconductor layers are formed over the substrate 300 in thePFET region 301 and the NFET region 303 respectively. The first stack305 and stack 307 of semiconductor layers may include alternating layersof different compositions. For example, in some embodiments, the firstand second stacks 305 and 307 include first semiconductor layers 306 ofa first composition alternating with second semiconductor layers 308 ofa second composition different from the first composition. By way ofexample, the first semiconductor layer 306 is made of SiGe, and thesecond semiconductor layer 308 is made of Si. In some embodiments wherethe substrate 300 is silicon and the semiconductor layer 306 is made ofSiGe, epitaxy conditions of forming a bottommost SiGe layer 306 can becontrolled such an incubation time of epitaxially growing SiGe on Si(i.e. heteroepitaxial growth) is longer than an incubation time ofepitaxially growing SiGe on SiGe (i.e. homoepitaxial growth). In someembodiments, the formation of the bottommost SiGe layer 306 may beperformed at a temperature below about 600° C. to result in incubationtime difference between growing the SiGe on SiGe and growing SiGe on Si.As a result, a portion of the bottommost SiGe layer 306 grown on siliconin the PFET region 301 is thinner than a portion of the bottommost SiGelayer 306 grown on silicon germanium in the NFET region 303. Such athickness difference contributes to alignment of subsequently formed Sinanowires in the NFET region 303 with SiGe nanowires in the PFET region301.

By way of example, a thickness difference between the portion of thebottommost SiGe layer 306 in the PFET region 301 and that in the NFETregion 303 is substantially equal to a thickness of each overlyingsemiconductor layers 306 and 308, which in turn will improve thealignment of nanowires in the PFET region 301 with nanowires in NFETregion 303. For example, the thickness difference between the portion ofthe bottommost SiGe layer 306 in the PFET region 301 and that in theNFET region 303 is in a range from about 4 nm to about 10 nm.

Referring to FIG. 31, first and second fin elements 310A and 310B areformed over the PFET region 301 and the NFET region 303 using suitableprocesses including photolithography and etch processes. In someembodiments, a photoresist is formed over the first and second stacks305 and 307 (as shown in FIG. 30) and patterned using a lithographyprocess. The patterned photoresist may then be used to protect regionsof the substrate 300 and the SiGe layer 304, and layers formedthereupon, while an etch process forms trenches in unprotected regionsthrough the photoresist, through the stacks 305 and 307, and into thesubstrate 300 and the SiGe layer 304. The remaining portions of thestacks 305 and 307 can serve as fin elements 310A and 310B that includethe semiconductor layers 306 and 308. In some embodiments, the patternsin photoresist are controlled so as to result in a desired width of thefin elements 310A and 310B. The width may be chosen based on deviceperformance considerations. In some embodiments, the first fin element310A is a portion of P-type metal-oxide semiconductor (PFET) devices,and the second fin element 310B is a portion of N-type metal-oxidesemiconductor (NFET) devices. As illustrated in FIG. 31, the first finelement 310A extends upwardly from the PFET region 301, and the secondfin element 310B extends upwardly from the PFET region 301.

Isolation regions 309 are formed, as shown in FIG. 31. A dielectricmaterial, such as silicon oxide, may be deposited into the trenchesbetween the fin elements to form isolation regions 309. A chemicalmechanical planarization (CMP) operation may be performed to planarize atop surface of the isolation regions 309, and then the isolation regions309 are recessed, thereby leaving the fin elements 310A and 310Bextending above the isolation regions 309.

Referring to FIG. 32, the second semiconductor layers 308 in the PFETregion 301 and the first semiconductor layers 306 in the NFET region 303are removed using suitable etch techniques. For example, the secondsemiconductor layers 308 in the PFET region 301 are removed by using afirst etching process, and the first semiconductor layers 306 in theNFET region 303 are removed by using a second etching process differentfrom the first etching process. In some embodiments, an etch rate ofsilicon is greater than an etch rate of silicon germanium during thefirst etching process, so that the silicon layers 308 in the PFET region301 are selectively removed. On the contrary, an etch rate of silicongermanium is greater than an etch rate of silicon during the secondetching process, so that the silicon germanium layers 306 in the NFETregion 303 are selectively removed. Embodiments of the presentdisclosure may employ a patterned mask to protect a region (e.g. NFETregion 303) when certain semiconductor layers in another region (e.g.PFET region 301) are to be removed.

In the following discussion, the remaining semiconductor layers 306 ofthe fin elements 310A are referred to as first nanowires 316A. In someembodiments, as shown in FIG. 32, the nanowires 316A have across-sectional profile of a rectangle and are suspended. Gaps 317A areformed between adjacent nanowires 316A. In addition, immediatelyadjacent nanowires 316A are spaced-apart by a substantially equaldistance.

In the following discussion, the remaining semiconductor layers 308 ofthe fin elements 310B in the NFET region 303 are referred to as thenanowires 316B. In some embodiments, as shown in FIG. 32, nanowires 316Bhave a cross-sectional profile of a rectangle and are suspended.Immediately adjacent nanowires 316B may be spaced-apart by gaps 317Bformed between adjacent nanowires 316B. In addition, immediatelyadjacent nanowires 316B are spaced-apart by a substantially equaldistance. The nanowires 316A in the PFET region 301 are aligned with thenanowires 316B in the NFET region 303, as shown in FIG. 32, which inturn will reduce potential loading effects in subsequent processes (e.g.formation of gate stacks).

Next, a first gate stack 322A is formed around each first nanowires316A, and a second gate stack 322B is formed around each second nanowire316B. The gate stacks are formed around a central portion of thenanowires that is channel regions of the nanowires. The gate stack 322Aincludes a gate dielectric layer 318A formed around nanowires 316A and agate electrode layer 320A formed around the gate dielectric layer 318A,in some embodiments. The gate stack 322B includes a gate dielectriclayer 318B formed around nanowires 316B and a gate electrode layer 320Bformed around the gate dielectric layer 318B, in some embodiments.

In certain embodiments, at least one of the gate dielectric layers 318Aand 318B includes one or more layers of a dielectric material, asdiscussed with respect to the gate dielectric layers 118A and 118B. Atleast one of the gate electrode layers 320A and 320B includes one ormore layers of conductive material, as discussed with respect to thegate electrode layer 120A and 120B.

In some embodiments, insulating sidewalls 319 are formed on opposingsides of the gate stacks 322A and 322B, and first source/drain layers315A are formed on peripheral portions of the nanowires 316A and onopposing sides of the gate stack 322A. The insulating sidewall 319 isbetween the gate stack 322A and the source/drain layer 315A, as shown inFIG. 34, which corresponds to a cross section according to line B-B ofFIG. 25 of the first nanowire structure 324A. Similarly, secondsource/drain layers 315B are formed on peripheral portions of thenanowires 316B and on opposing sides of the gate stack 322B. Theinsulating sidewall 319 is between the gate electrode layer 320B and thesource/drain layer 315B, as shown in FIG. 35, which corresponds to across section according to line C-C of FIG. 25 of the second nanowirestructure 324B.

By way of example, the material for the source/drain layers 315Aincludes one or more layers of Ge or SiGe suitable for the PFET device,and material for the source/drain layers 315B includes one or morelayers of Si, SiP, or SiC suitable for the NFET device. The source/drainlayers 315A and 315B are formed by an epitaxial growth method using CVD,ALD, or molecular beam epitaxy (MBE). During formation of thesource/drain layer 315A for the PFET device, the second nanowires 316Bin the NFET region 303 are covered by a patterned mask. During formationof the source/drain layer 315B for the NFET device, the first nanowires316A of the PFET device are covered by another patterned mask.

In order to support the nanowires during processing, the peripheralportions of the nanowires where the source/drain layers 315A and 315Bare formed may be masked during the removal of either the first andsecond semiconductor layers 306 and 308 from the central portions of thenanowires where the gate stacks 322A and 322B are to be formed. Afterformation of the gate stacks 322A and 322B, the central portion of thenanowires where the gate stacks 322A and 322B are formed may be masked,and the respective first and second semiconductor layers 306 and 308 areremoved from the peripheral portions of the nanowire where thesource/drain layers 315A and 315B are formed.

Alternatively, in some embodiments dummy gate structures are initiallyformed on the first and second fin elements 310A and 310B (see FIG. 31),and the respective first and second semiconductor layers 306 and 308 areremoved from the peripheral portions of the nanowire where thesource/drain layers 315A and 315B are formed. After forming thesource/drain layers 315A and 315B, the dummy gate electrode structuresare removed, followed by formation of gate stacks 322A and 322Baccording to the present disclosure.

The embodiments of the present disclosure offer advantages over existingart, although it is understood that different embodiments may offerdifferent advantages, not all advantages are necessarily discussedherein, and that no particular advantage is required for allembodiments. By utilizing the method as discussed above, the loadingeffect in formation of gate stacks (e.g., gate stacks 122A, 122B, 222A,222B, 322A and/or 322B) are reduced because nanowires in NFET region aresubstantially aligned with respective nanowires in PFET region.

In accordance with some embodiments, a method for forming asemiconductor device is provided. The method includes forming a firstrecess in a substrate. The method includes forming a first semiconductorlayer into the first recess. The first semiconductor layer and thesubstrate are made of different materials, and a first top surface ofthe first semiconductor layer is lower than a second top surface of thesubstrate. The method includes forming a second semiconductor layer overthe first top surface and the second top surface, wherein a third topsurface of the second semiconductor layer over the first top surface issubstantially level with the second top surface of the substrate, andthe second semiconductor layer and the substrate are made of differentmaterials. The method includes forming a third semiconductor layer overthe second semiconductor layer. The third semiconductor layer and thesecond semiconductor layer are made of different materials.

In accordance with some embodiments, a method for forming asemiconductor device is provided. The method includes forming a firstrecess in a substrate. The method includes forming a first semiconductorlayer into the first recess. The first semiconductor layer and thesubstrate are made of different materials, and a first top surface ofthe first semiconductor layer is higher than a second top surface of thesubstrate. The method includes forming a second semiconductor layer overthe first top surface and the second top surface, wherein a third topsurface of the second semiconductor layer over the second top surface issubstantially level with the first top surface of the firstsemiconductor layer, and the second semiconductor layer and thesubstrate are made of different materials. The method includes forming athird semiconductor layer over the second semiconductor layer. The thirdsemiconductor layer and the second semiconductor layer are made ofdifferent materials.

In accordance with some embodiments, a semiconductor device is provided.The semiconductor device includes a substrate comprising a first baseportion and a first fin portion over the first base portion. Thesemiconductor device includes a semiconductor layer partially embeddedin the substrate. The semiconductor layer includes a second base portionand a second fin portion over the second base portion, a first topsurface of the first fin portion is substantially coplanar with a secondtop surface of the second fin portion, and the semiconductor layer andthe substrate are made of different materials. The semiconductor deviceincludes a first strip structure over the first fin portion. The firststrip structure and the substrate are made of different materials. Thesemiconductor device includes a second strip structure over the secondfin portion. The second strip structure and the semiconductor layer aremade of different materials. The semiconductor device includes a firstgate stack over the substrate and surrounding the first strip structure.The semiconductor device includes a second gate stack over thesemiconductor layer and surrounding the second strip structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a semiconductor device,comprising: forming a first recess in a substrate; forming a firstsemiconductor layer into the first recess, wherein the firstsemiconductor layer and the substrate are made of different materials,and a first top surface of the first semiconductor layer is lower than asecond top surface of the substrate; forming a second semiconductorlayer over the first top surface and the second top surface, wherein athird top surface of the second semiconductor layer over the first topsurface is substantially level with the second top surface of thesubstrate, and the second semiconductor layer and the substrate are madeof different materials; and forming a third semiconductor layer over thesecond semiconductor layer, wherein the third semiconductor layer andthe second semiconductor layer are made of different materials.
 2. Themethod for forming the semiconductor device as claimed in claim 1,wherein a height difference between the first top surface and the secondtop surface is substantially equal to a thickness of the secondsemiconductor layer over the first top surface of the firstsemiconductor layer.
 3. The method for forming the semiconductor deviceas claimed in claim 1, wherein the second semiconductor layerconformally covers the first top surface and the second top surface, andthe third semiconductor layer conformally covers the secondsemiconductor layer.
 4. The method for forming the semiconductor deviceas claimed in claim 1, wherein the first semiconductor layer and thesecond semiconductor layer are made of a same first material.
 5. Themethod for forming the semiconductor device as claimed in claim 4,wherein the substrate and the third semiconductor layer are made of asame second material.
 6. The method for forming the semiconductor deviceas claimed in claim 5, wherein the first material comprises silicongermanium, and the second material comprises silicon.
 7. The method forforming the semiconductor device as claimed in claim 1, furthercomprising: partially removing the third semiconductor layer, the secondsemiconductor layer, the first semiconductor layer, and the substrate toform second recesses in the third semiconductor layer, the secondsemiconductor layer, the first semiconductor layer, and the substrate,wherein the second recesses pass through the third semiconductor layerand the second semiconductor layer and extend into the firstsemiconductor layer and the substrate, a first fin element and a secondfin element are between the second recesses, the first fin elementcomprises a first portion of the substrate, a second portion of thesecond semiconductor layer, and a third portion of the thirdsemiconductor layer, and the second fin element comprises a fourthportion of the first semiconductor layer, a fifth portion of the secondsemiconductor layer, and a sixth portion of the third semiconductorlayer.
 8. The method for forming the semiconductor device as claimed inclaim 7, further comprising: forming an isolation structure in thesecond recesses, wherein a fourth top surface of the isolation structureis lower than the first top surface of the first semiconductor layer. 9.The method for forming the semiconductor device as claimed in claim 8,further comprising: removing the first portion of the substrate outsideof the isolation structure, the third portion of the third semiconductorlayer, the fourth portion of the first semiconductor layer outside ofthe isolation structure, and the fifth portion of the secondsemiconductor layer.
 10. The method for forming the semiconductor deviceas claimed in claim 9, further comprising: forming a first gate stackover the substrate and the isolation structure and surrounding thesecond portion of the second semiconductor layer; and forming a secondgate stack over the first semiconductor layer and the isolationstructure and surrounding the sixth portion of the third semiconductorlayer.
 11. A method for forming a semiconductor device, comprising:forming a first recess in a substrate; forming a first semiconductorlayer into the first recess, wherein the first semiconductor layer andthe substrate are made of different materials, and a first top surfaceof the first semiconductor layer is higher than a second top surface ofthe substrate; forming a second semiconductor layer over the first topsurface and the second top surface, wherein a third top surface of thesecond semiconductor layer over the second top surface is substantiallylevel with the first top surface of the first semiconductor layer, andthe second semiconductor layer and the substrate are made of differentmaterials; and forming a third semiconductor layer over the secondsemiconductor layer, wherein the third semiconductor layer and thesecond semiconductor layer are made of different materials.
 12. Themethod for forming the semiconductor device as claimed in claim 11,further comprising: partially removing the third semiconductor layer,the second semiconductor layer, the first semiconductor layer, and thesubstrate to form second recesses in the third semiconductor layer, thesecond semiconductor layer, the first semiconductor layer, and thesubstrate, wherein the second recesses pass through the thirdsemiconductor layer and the second semiconductor layer and extend intothe first semiconductor layer and the substrate, a first fin element anda second fin element are between the second recesses, the first finelement comprises a first portion of the substrate, a second portion ofthe second semiconductor layer, and a third portion of the thirdsemiconductor layer, and the second fin element comprises a fourthportion of the first semiconductor layer, a fifth portion of the secondsemiconductor layer, and a sixth portion of the third semiconductorlayer.
 13. The method for forming the semiconductor device as claimed inclaim 12, further comprising: forming an isolation structure in thesecond recesses, wherein a fourth top surface of the isolation structureis lower than the first top surface of the first semiconductor layer.14. The method for forming the semiconductor device as claimed in claim13, further comprising: removing the third portion of the thirdsemiconductor layer, the fourth portion of the first semiconductor layeroutside of the isolation structure, and the fifth portion of the secondsemiconductor layer.
 15. The method for forming the semiconductor deviceas claimed in claim 14, further comprising: forming a first gate stackover the substrate and the isolation structure and wrapping the secondportion of the second semiconductor layer; and forming a second gatestack over the first semiconductor layer and the isolation structure andwrapping the sixth portion of the third semiconductor layer.
 16. Asemiconductor device, comprising: a substrate comprising a first baseportion and a first fin portion over the first base portion; asemiconductor layer partially embedded in the substrate, wherein thesemiconductor layer comprises a second base portion and a second finportion over the second base portion, a first top surface of the firstfin portion is substantially coplanar with a second top surface of thesecond fin portion, and the semiconductor layer and the substrate aremade of different materials; a first strip structure over the first finportion, wherein the first strip structure and the substrate are made ofdifferent materials; a second strip structure over the second finportion, wherein the second strip structure and the semiconductor layerare made of different materials; a first gate stack over the substrateand surrounding the first strip structure; and a second gate stack overthe semiconductor layer and surrounding the second strip structure. 17.The semiconductor device as claimed in claim 16, wherein the first stripstructure and the second strip structure are made of differentmaterials.
 18. The semiconductor device as claimed in claim 16, whereina third top surface of the first strip structure and a fourth topsurface of the second strip structure are substantially coplanar. 19.The semiconductor device as claimed in claim 16, further comprising: anisolation structure between the first fin portion and the second finportion and over the first base portion and the second base portion. 20.The semiconductor device as claimed in claim 19, wherein a third topsurface of the isolation structure, the first top surface of the firstfin portion, and the second top surface of the second fin portion aresubstantially coplanar.